Solvent dyeing of anodized aluminum



K. H. DALE April 22, 1969 SOLVEN'I' DYEING OF ANODZED ALUMINUM- FiledJune l5, 1966 KENNETH H. DALE United States Patent O 3 440 111 soLvENTDvErNG 6F NoDIzED ALUMINUM Kenneth Howard Dale, Henrico County, Va.,assignoit` to Reynolds Metals Company, Richmond, Va., a corporation ofDelaware Filed .lune 15, 1966. Ser. No. 557,648 Int. Cl. C23f 5/04; B44d1/34 U.S. Cl. 14S-6.1 15 Claims This invention relates to a novel methodfor dyeing anodized aluminous metals. More particularly, the inventionconcerns a system for the continuous dyeing of anodized aluminum,including a novel dye solvent removal and drying sequence.

It has long been known that anodized aluminum and aluminum base alloyscan be dyed or colored by the application to the aluminum oxide coatingof aqueous solutions of water soluble dyes, but colors produced in thisway are deficient in light and heat f-astness and have a `tendencytoward streaking. Hence it has been proposed in the prior art to employfor this purpose, spirit soluble dyes dissolved in alcohol or acetone ormixtures thereof. However, the water miscibility of these solventsresults in the same shortcomings as in the case of water soluble dyes.Hence, it has been further proposed to utilize waterinsoluble dyes orcolorants dissolved in water immisc-i'ble organic solvents, especiallyhigh boiling halogenated aromatic hydrocarbon solvents, for dyeinganodized aluminum, and `a system of this type is described in U.S.Patent No, 2,975,081.

Experience has shown, however, that in a system employing suchwater-immiscible organic solvents, the l'ow volatility of these solventsmakes their removal from the dyed aluminum, and their recovery forreuse, expensive and difficult. Nevertheless, the complete removal ofthe dye solvent from the work after dyeing and before sealing of thedyed anodized article is essential to insure successtul dyeing.

In accordance with the present invention, there is pr-ovided a rapid,economical, and continuous meth-od for dyeing anodized aluminum, whichemploys a novel multiple solvent system for removal or stripping of thedye solvent from the dyed anodized aluminum, utilizing for this purposea second, or stripping solvent, which is miscible with the dye solvent,but which will not dissolve or attack the dye itself, and will leave thedye in place and intact on the anodized article. Thus, the dyeing methodof the invention necessitates the use of organic dyestuls which aresoluble in the dye solvent, but which are insoluble in the strippingsolvent. The dyes employed in the practice of the invention Willgenerally be oil soluble or spirit soluble dyes, but may even includeWater soluble dyes if the latter are capable of meeting the conditionsof solubility in the dye solvent, and of ins-olubility in the strippingsolvent.

There are employed as dye solvents, in accordance with the invention,organic, `water-immi'scible solvents, which may be either acyclic orcyclic, or mixtures of such solvents. Thus, there may be employedhalogenated hydrocarbons, such as carbon tetrachloride and methylenechloride, polyhydroxy compounds such as diethylene glycol alkyl ethers,alkyl derivatives of aliphatic acid amides, such as dimethylformamide,diethylformamide, dimethylacetamide, diethylacetamide, and the like, anddimethylsulfoxide. Examples of cyclic and aromatic organic sol-3,440,111 Patented Apr. 22, 1969 vents include quinoline, benzylalcohol, nitrobenzene and halogenated benzenes, such as the chlorinatedbenzenes, including for example, chlorobenzene, orthodichlorobenzene,paradichlorobenzene, tetrachlorobenzene, and the like. Preferably thereis used as a dye solvent a mixture of chlorinated benzenes knowncommercially as Polychlorobenzene, which includes penta, tetra-, triandmonochlorobenzene, as well as some oand p-dichlorobenzene.

As a dye solvent removal or stripping agent, in accordance with theinvention, there is advantageously employed a fluorinated aliphatichydrocarbon containing at least three iluorine atoms. A preferred groupof such stripping solvents is that of the chlorinated and fluorinatedaliphatic hydrocar-bons which contain at least three norine atoms, andwhich are volatile, nontoxic, and noninflammable. Examples of suchstripping solvents include:

Monochlorotriuoromethane (Freon 13), CCl`F3,

BJP. l'l4.\6 F. l,l,Z-trichloro-1,2,2-trifluoroethane (Freon ll3),

OCl2FC'ClF2, B.P. 117.6" F. sym-dichlorotetrafluoroethane, CClFZCClFg,B.P. 38.4 F. 1,2-dichloro-l,`l,2,2tetralluoroethane (Freon `114),

BEP. 4.l F.

These fluorinated compounds are miscible with the types of dye solventsmentioned above.

It has been found that for successful dye solvent stripping, thefluorinated compound must contain at least three luorine atoms. lFewerthan three fluorine atoms produce streaking elfects by attack of thestripping solvent on the dyes themselves, possibly owing to the presenceof chlorine atoms in the molecule. Such streaking is produced, forexample, by compounds such as trichlorom-onouoroethane andtetrachlorodilluoroethane, which contain only one or two uorine atoms.The presence of three or more fluorine atoms in the molecule is believedto suppress the solubilizing action of the chlorine atoms on thedyestuif molecule.

The oil soluble and spirit dyes which have the additional characteristicof being insoluble in the stripping agents, as explained previously,include both dyestuffs and dye intermediates which are members of theazo, anthraquinone, indigo, thioindigo, phthalocyanine classes of dyes.Speciic examples of such dyes include:

Red Violet PH Pigment Violet 19 (CJ. 46500) Prior to the application ofthe dye and dye solvent, the anodized article must be thoroughly washedto remove all traces of the anodizing electrolyte, and must be fullydried. This may be conveniently accomplished by Water rinsing, followedby removal of the Water by treatment of the wet anodized article with anorganic solvent, such as a chlorinated aliphatic hydrocarbon solvent,which is capable of forming a constant boiling mixture or azeotrope withthe water. Examples of such solvents include trichloroethylene, ethylenedichloride, propylene dichloride, and the like, trichloroethylene beingpreferred for this purpose. The trichloroethylene preferably contains awetting agent or surfactant, and is applied to the anodized article atan elevated temperature, for example, at a temperature of about 180 to250 F., for a period of about 30 to 50' seconds. The hot solventextracts the water to form a constant boiling mixture having a boilingpoint (163 o 1&37" F.) lower than that of water or of trichloroethylene(187 F.), and is vaporized. The trichloroetylene-water vapor mixture iscondensed, and the trichloroethylene is recovered and recycled to thedrying operation.

The novel method of the invention for dyeing anodized aluminum thereforecomprises the steps of (a) removing water from a wet anodized aluminumarticle by applying to the article an organic solvent capable of forminga constant boiling mixture with the water present, at an elevatedtemperature; (b) applying to the dry anodized aluminum surface asolution of a dyestuff in a water immiscible organic dye solvent toproduce a color thereon; and (c) removing and recovering said dyesolvent from the dyed but solvent wet article and drying said article bytreating the article with an organic stripping solvent which is misciblewith the dye solvent but which is not a solvent for the dye. Theforegoing method may be operated continuously, with all solvents beingcontinuously recovered and reused.

After removal of solvents and drying of the dyed articles, the coloredanodized coating may be sealed by conventional sealing methods,including hot water, cobaltnickel acetate solution, chlorinatedparaffin, alkali metal dichromates, and the like.

The practice of the invention will be more fully understood by referenceto the accompanying drawing which illustrates a form of apparatussuitable for performing the method, but which is not to be regarded aslimiting.

In the drawing, there is shown schematically an arrangement of threecomponents, of which 1 designates a unit for the drying of wet anodizedaluminum articles with an organic solvent, with provision for recoveryof the solvent. The unit comprises a divided tank 2 separated into twoportions by partition 3, and provided at its upper end with condensers 4and 5, and at its lower portion with heating coils 6 and 7. The waterwet anodized aluminum part is placed in first section the water removalunit where it is contacted with hot (180- 190 F.) trichloroethylenecontaining a surfactant, either by immersion or curtain flowing for30-50 seconds. The solution is vaporized and the vapor collects asliquid on the condensing coils and is caught in troughs 8 below thecoils and Hows to water separator 9 where water is extracted and thetrichloroethylene is returned to the drying solution. The water-freeanodized article is then transferred to the second section 11 of thetank for about 30 seconds. This section contains hot liquid-vaportrichloroethylene, wherein the article is further cleaned and dried bythe hot vapor, and any residual surfactant is removed.

The water-free, dry anodized article is then transferred to the dyeapplication unit 12 where the article is contacted by a hot solution ofdyestuff by owing, curtain coating or spraying. The dye applicationunit, in the form shown, is provided with a pump 13, heating means |14,and spray circulation system 15. The bulk of solvent may be recovered bya suitable system, such as an alumina absorption column, not shown.

The solvent-wet, dyed anodized article is then transferred to a solventdrying-recovery unit 16 where stripping of the dye solvent takes place.This is done by contacting the article for 30-40 seconds by a hot (110-115 F.) solvent which has selective solubility or miscibility for thedye solvent and in which the dye is substantially insoluble. This unitis also provided with partition 17, and with heating coils 17 and A18,and condensers 19 and 20. The warm stripping solvent vapors remove thedye solvent and dry the article, while the two solvents are collected inthe sump of the unit. The stripping solvent is distilled over at about-140 F. when it becomes enriched with dye solvent, and afterdistillation, the recovered dye solvent can be returned to the dyeapplication unit. The solvent-free, dry, dyed anodized article is thenready for sealing by any conventional method.

The following example illustrates the performance of the method, but isnot to be regarded as limiting:

Example A panel of aluminum alloy 1030 was cleaned, etched, and anodizedfor 60 minutes in 15% sulfuric acid at 70 F. at a current density of 12amperes per sq. ft., and rinsed with water. The panel was dried withtrichloroethylene containing a surfactant at F. for 40 seconds. The drypanel was dyed for 20 minutes in a solution of Golden Yellow LG dyestuffin orthodichlorobenzene at 70 C. in a concentration of 4 g. per liter.The panel was dried by treatment with trichloro triuoroethane at 100-115F. for 30-40 seconds, to effect removal of residualorthodichlorobenzene. The article was then sealed in boiling water for20 minutes. The sample was heated to 300 C. in an oven for 1 hour,cooled to room temperature, heated to 400 C. for 30 minutes, and cooled.It retained its original dyed shade and showed no heat fading.

What is claimed is:

1. Method for dyeing anodized aluminum comprising the steps of: (a)removing water from a wet anodized aluminum article by applying to thearticle an organic dehyrating solvent capable of forming a constantboiling mixture with the water present, at an elevated temperature; (b)applying to the dry anodized aluminum surface a solution of a dyestutfin a water-immiscible organic dye solvent to produce a color thereon;and (c) removing and recovering said dye solvent from the dyed butsolvent-wet article and drying said article by treating the article withan organic stripping solvent which is miscible with the dye solvent butwhich is not a solvent for the dye.

2. The method of claim 1 which includes the further step of sealing thedyed anodized coating.

3. The method of claim -1 in which the dehydrating solvent istrichloroethylene.

4. The method of claim 1 in which the stripping solvent is a fluorinatedaliphatic hydrocarbon containing at least three iluorine atoms.

5. The method of claim 1 in which thc dye solvent is a chlorinatedbenzene.

6. Method for dyeing anodized aluminum comprising the steps of (a)applying to a dry anodized aluminum surface a solution of a dyestutf ina water-immiscible organic dye solvent to produce a color thereon; and(b) removing and recovering said dye solvent from the dyed butsolventwet aluminum and drying said aluminum by treating it with anorganic stripping solvent which is miscible with the dye solvent butwhich is not a solvent for the dye.

7. In the method for dyeing anodized aluminum including applying to thedry anodized aluminum surface a solution of a dyestuff in awater-immiscible organic dye solvent to produce a color thereon, theimprovement which comprises removing and recovering said dye solventfrom the dyed but solvent-wet aluminum and drying said aluminum bytreating it with an organic stripping solvent which is miscible with thedye solvent but which is not a solvent for the dye.

8. The method of claim 7 in which stripping solvent is a fluorinatedaliphatic hydrocarbon containing at least three uorine atoms.

9. The method of claim t8 in which the stripping solvent is afluorinated and chlorinated aliphatic hydrocarbon containing at least 3fluorine atoms.

10. The method of claim 6 in which the dye is an oil soluble dye.

y11. The method of claim `6 in which the dye solvent is a chlorinatedbenzene.

6 12. The method of claim 6 in which the stripping sol- References Citedvent is a `iluorinated aliphatic hydrocarbon containing at UNITED STATESPATENTS least three fluorine atoms.

13. The method of claim 6 in which the stripping sol- 2975081 3/1961Klrby et al 148-61 vent is a fluorinated and chlorinated aliphatichydrOcar- 5 Dssaner 148-6'1 bon containing at least three :fluorineatoms. 5 Klrby et al 148-6'1 `14. The method of claim 6 in which the dyeis sub- RALPH S. KENDALL Primary Examiner stantially insoluble in thestripping solvent.

1s. The method of claim ,a in which is included the US C1- X-R- furtherstep of sealing the dyed anodized coating. 10 117-49, 62, 127; 204-35

1. METHOD FOR DYEING ANODIZED ALUMINUM COMPRISING THE STEPS OF: (A)REMOVING WATER FROM A WET ANODIZED ALUMINUM ARTICLE BY APPLYING TO THEARTICLE AN ORGANIC DEHYRATING SOLVENT CAPABLE OF FORMING A CONSTANTBOILING MIXTURE WITH THE WATER PRESENT, AT AN ELEVATED TEMPERATURE; (B)APPLYING TO THE DRY ANODIZED ALUMINUM SURFACE A SOLUTION OF A DYESTUFFIN A WATER-IMMISCIBLE ORGANIC DYE SOLVENT TO PRODUCE A COLOR THEREON;AND (C) REMOVING AND RECOVERING SAID DYE SOLVENT FROM THE DYED BUTSOLVENT-WET ARTICLE AND DRYING SAID ARTICLE BY TREATING THE ARTICLE WITHAN ORGANIC STRIPPING SOLVENT WHICH IS MISCIBLE WITH THE DYE SOLVENT BUTWHICH IS NOT A SOLVENT FOR THE DYE.